Post-tensioning is a method of applying prestress to concrete. In more detail, tendons are tensioned and anchored in concrete after the concrete has been cured to allow the tension forces to be introduced to the tendons.
A plurality of tendons are arranged in concrete beams or slabs, and in this case, it is important to minimize the deviation in the tension forces introduced to the plurality of tendons so as to allow the tension forces to be applied uniformly to the plurality of tendons. It is actually recommended that the error range between a designed tension force and a real tension force is controlled within the average of 7% and to the maximum of 13%.
In conventional post-tensioning, the tension force of the tendon is measured by reading the pressure gauge of a pressure pump and by measuring the moving distance of a piston of a hydraulic jack.
However, the conventional measuring methods are carried out in an analog way, thereby undesirably needing many labors in monitoring the tension forces of the tendons.
Further, the pressure gauge or the moving distance of the piston is measured by a checker, and at the same time, the buttons for stopping the tensioning are pressed manually to control the tension forces of the tendons, so that the tension forces of the tendons are differently applied every time. That is, there are many differences in the measurement and control of the tension forces, constructability, and working time according to the skill level of a worker, thereby making it difficult to conduct accurate tensioning.
Moreover, the elongation length of the tendon after the tensioning is measured by a ruler to check the error range, but the elongation lengths of the tendons may be different from each other according to the friction coefficients of the tendons or the lengths of steel strands, so that even if the elongation lengths are measured, there is no method of accurately recognizing the sizes of the tension forces applied to the tendons.
In addition, the pressure gauge data or the moving distance data of the piston and the elongation length data measured by the ruler are provided only by the record of the worker on the construction site, so that only the values on the record exist as database.
Accordingly, it is impossible to accurately measure the tension forces of the tendons so that error control is meaningless.